Yamaha YFM125S User manual

YFM125S
3FA-AE2
SUPPLEMENTARY
SERVICE MANUAL

FOREWORD
This Supplementary Service Manual has been prepared to introduce new service and data for the
YFM125S. For complete service information procedures it is necessary to use this Supplementary
Service Manual together with the following manual.
YFA1W SERVICE MANUAL: 3FA-ME1
YFA1(P) 2002 SUPPLEMENTARY SERVICE MANUAL: 3FA-AE1
YFM125S
SUPPLEMENTARY
SERVICE MANUAL
©2004 by Yamaha Motor Co., Ltd.
First edition, January 2004
All rights reserved.
Any reproduction or unauthorized use
without the written permission of
Yamaha Motor Co., Ltd.
is expressly prohibited.

EBS00002
NOTICE
This manual was produced by the Yamaha Motor Company primarily for use by Yamaha dealers
and their qualified mechanics. It is not possible to include all the knowledge of a mechanic in one
manual, so it is assumed that anyone who uses this book to perform maintenance and repairs on
Yamaha machine has a basic understanding of the mechanical ideas and the procedures of
machine repair. Repairs attempted by anyone without this knowledge are likely to render the
machine unsafe and unfit for use.
Yamaha Motor Company, Ltd. is continually striving to improve all its models. Modifications and sig-
nificant changes in specifications or procedures will be forwarded to all authorized Yamaha dealers
and will appear in future editions of this manual where applicable.
NOTE:
_
Designs and specifications are subject to change without notice.
EBS00003
IMPORTANT INFORMATION
Particularly important information is distinguished in this manual by the following notations.
The Safety Alert Symbol means ATTENTION! BECOME ALERT! YOUR
SAFETY IS INVOLVED!
Failure to follow WARNING instructions could result in severe injury or death
to the machine operator, a bystander or a person checking or repairing the
machine.
A CAUTION indicates special precautions that must be taken to avoid dam-
age to the machine.
A NOTE provides key information to make procedures easier or clearer.
WARNING
CAUTION:
NOTE:

EBS00004
HOW TO USE THIS MANUAL
MANUAL ORGANIZATION
This manual consists of chapters for the main categories of subjects. (See “symbols”)
1st title 1: This is the title of the chapter with its symbol in the upper right corner of each page.
2nd title 2: This title indicates the section of the chapter and only appears on the first page of each
section. It is located in the upper left corner of the page.
3rd title 3: This title indicates a sub-section that is followed by step-by-step procedures accompa-
nied by corresponding illustrations.
EXPLODED DIAGRAMS
To help identify parts and clarify procedure steps, there are exploded diagrams at the start of each
removal and disassembly section.
1. An easy-to-see exploded diagram 4is provided for removal and disassembly jobs.
2. Numbers 5are given in the order of the jobs in the exploded diagram. A number that is enclosed
by a circle indicates a disassembly step.
3. An explanation of jobs and notes is presented in an easy-to-read way by the use of symbol marks
6. The meanings of the symbol marks are given on the next page.
4. A job instruction chart 7accompanies the exploded diagram, providing the order of jobs, names
of parts, notes in jobs, etc.
5. For jobs requiring more information, the step-by-step format supplements 8are given in addition
to the exploded diagram and the job instruction chart.

EB003000
ILLUSTRATED SYMBOLS
Illustrated symbols 1to 8are printed on the
top right of each page and indicate the subject
of each chapter.
1General information
2Specifications
3Periodic checks and adjustments
4Engine
5Carburetion
6Chassis
7Electrical
8Troubleshooting
Illustrated symbols 9to Eare used to identify
the specifications appearing in the text.
9Filling fluid
0Lubricant
ASpecial tool
BTorque
CWear limit, clearance
DEngine speed
EΩ, V, A
Illustrated symbols Fto Lin the exploded
diagrams indicate the types of lubricants and
lubrication points.
FApply engine oil
GApply gear oil
HApply molybdenum disulfide oil
IApply wheel bearing grease
JApply lightweight lithium soap base grease
KApply molybdenum disulfide grease
LApply silicon grease
Illustrated symbols Mto Nin the exploded
diagrams indicate where to apply a locking
agent Mand when to install a new part N.
MApply the locking agent (LOCTITE®)
NReplace
12
34
56
78
90
AB
CD
E
FGH
I
MN
GEN
INFO SPEC
CHK
ADJ ENG
CARB CHAS
–+
ELEC TRBL
SHTG
T
R
.
.
EGM
BLS MS
JKL
LT
New

CONTENTS
SPECIFICATIONS ............................................................................................1
GENERAL SPECIFICATIONS ..................................................................1
MAINTENANCE SPECIFICATIONS .........................................................2
ENGINE ................................................................................................2
CHASSIS ..............................................................................................2
ELECTRICAL ........................................................................................3
CABLE ROUTING .....................................................................................4
PERIODIC CHECKS AND ADJUSTMENTS ..................................................17
SEAT, CARRIERS AND FENDERS ........................................................17
SEAT, FRONT CARRIER, FRONT BUMPER AND CENTER COVER ....17
FRONT GRILL ASSEMBLY AND FRONT FENDER ..........................19
REAR CARRIER AND REAR FENDER ..............................................20
ELECTRICAL ..........................................................................................22
ADJUSTING THE HEADLIGHT BEAMS ............................................22
REPLACING A HEADLIGHT BULB ....................................................22
ELECTRICAL .................................................................................................24
IGNITION SYSTEM .................................................................................24
CIRCUIT DIAGRAM ............................................................................24
CHARGING SYSTEM .............................................................................25
CIRCUIT DIAGRAM ............................................................................25
LIGHTING SYSTEM ................................................................................26
CIRCUIT DIAGRAM ............................................................................26
TROUBLESHOOTING ........................................................................27
SIGNAL SYSTEM ...................................................................................29
CIRCUIT DIAGRAM ............................................................................29
CHECKING THE SIGNALING SYSTEM .............................................30
YFM125S WIRING DIAGRAM

–1 –
SPEC
SPECIFICATIONS
GENERAL SPECIFICATIONS
Model YFM125S
Model code number 1C51: (for Oceania)
1C53: (for CDN)
1C54: (for Europe)
Dimensions
Overall length 1,710 mm (67.3 in)
Overall width 990 mm (39.0 in)
Overall height 980 mm (38.6 in)
Seat height 705 mm (27.8 in)
Wheelbase 1,080 mm (42.5 in)
Minimum ground clearance 145 mm (5.7 in)
Basic weight
Wet (with oil and a full fuel tank) 152 kg (335 lb)
Dry (without oil and fuel) 144 kg (317 lb)
Maximum load (except vehicle) 100 kg (220 lb)
Fuel
Type Regular unleaded gasoline only (for CDN and
Europe)
Unleaded gasoline only (for Oceania)
Fuel tank capacity 7.6 L (1.67 Imp gal, 2.01 US gal)
Reserve amount 1.3 L (0.28 Imp gal, 0.34 US gal)
Spark plug
Type/manufacturer CR7HS/NGK
Spark plug gap 0.6 ~ 0.7 mm (0.024 ~ 0.028 in)
Electrical
Ignition system DC C.D.I.
Generator system A.C. magneto generator
Battery capacity 12V 12Ah
Battery type 12N12C-4A-2
Headlight type Bulb type
Headlight bulb type Krypton
Bulb wattage (quantity)
Headlight 12 V 30 W/30 W (2 pc.)
Tail/brake light 12 V 5 W/21 W (1 pc.)
Neutral indicator light 12 V 1.7 W (1 pc.)
Reverse indicator light 12 V 1.7 W (1 pc.)
GENERAL SPECIFICATIONS

–2 –
SPEC
MAINTENANCE SPECIFICATIONS
MAINTENANCE SPECIFICATIONS
ENGINE
CHASSIS
Tightening torques
Model YFM125S
Carburetor
I.D. mark 5VJ2 10
Main jet (M.J) # 77.5
Main air jet (M.A.J) ø1.3
Jet needle (J.N) 4HPY46-1
Needle jet (N.J) O-1M
Cutaway (C.A) 2.5
Pilot air jet (P.A.J) # 130
Pilot outlet (P.O) ø0.7
Pilot jet (P.J) # 12.5
Bypass 1 (B.P.1) 1.1
Pilot screw (P.S) 2 and 1/2 turns out (for Europe and Oceania)
Valve seat size (V.S) 1.8
Starter jet (G.S) # 45
Fuel level (F.L) 3.5 ~ 4.5 mm (0.14 ~ 0.18 in)
With special tool
Engine idling speed 1,650 ~ 1,750 r/min
Intake vacuum 26.7 kPa (200 mmHg, 7.88 inHg)
Part to be tightened Thread size Tightening torque Remarks
Nm m ·kg ft ·lb
Footrest board and footrest bracket M5 7 0.7 5.1
Footrest and footrest bracket M6 10 1.0 7.2
Front fender and frame M6 7 0.7 5.1
Front carrier and front grill M6 7 0.7 5.1
Fuel tank M6 10 1.0 7.2

–3 –
SPEC
MAINTENANCE SPECIFICATIONS
ELECTRICAL
Model YFM125S
C.D.I.
Magneto model/manufacturer F1C5/YAMAHA
Pickup coil resistance 248 ~ 372 Ωat 20 °C (68 °F)
(lead color) (white-red)
C.D.I. unit model/manufacturer 3FA/YAMAHA
Charging system
Type A.C. magneto generator
Magneto model/manufacturer F1C5/YAMAHA
Charging coil resistance 0.8 ~ 1.2 Ωat 20 °C (68 °F)
(lead color) (white-white)
Charging current (Minimum) 6.2 A at 1,500 r/min
(Maximum) 13 A at 5,000 r/min
Standard output 14 V 150 W at 5,000 r/min
Rectifier/regulator
Model/manufacturer SH640E-11/SHINDENGEN
Regulator type Semi conductor short circuit type
No load regulated voltage (DC) 14.0 ~ 15.0 V
Rectifier capacity 14.0 A
Withstand voltage 200 V
Electric starting system
Type Constant mesh
Starter motor
Model/manufacturer 3FA/YAMAHA
Output 0.4 kW
Armature coil resistance 0.019 ~ 0.023 Ωat 20 °C (68 °F)
Overall length (brush) 10.0 mm (0.39 in)
<Limit> <3.5 mm (0.14 in)>
Brush spring pressure 552 ~ 828 g
Commutator diameter 22.0 mm (0.87 in)
<Wear limit> <21.0 mm (0.83 in)>
Mica undercut 1.5 mm (0.06 in)
Starter relay
Model/manufacturer MS5E-661/JIDECO
Amperage rating 100 A
Coil resistance 4.18 ~ 4.62 Ωat 20 °C (68 °F)
Starting circuit cut off relay
Model/manufacturer ACA12115-1/MATSUSHITA
Coil resistance 72 ~ 88 Ωat 20 °C (68 °F)
Diode No
Circuit breaker
Type Fuse
Amperage for individual circuit
Main 15 A

–4 –
SPEC
CABLE ROUTING
CABLE ROUTING
1Rear brake switch lead
2Rear brake cable
3Front brake cable
4Front brake switch lead
5Throttle cable
6Fuel tank breather hose
7Horn switch lead (for Europe)
8Horn switch (for Europe)
9Headlight lead (left)
0Headlight lead (right)
ANeutral/reverse indicator light lead
BMain switch lead
CCoupler cover
DSteering shaft
OFFRUN
ENG.STOP
LO
HI
0FF
LIGHTS
LIGHTS
0FF
HI
LO
ENG.STOP
OFF RUN
1 4
2 3
É
12
09
DC Ì
Ë
Í
A
B
Ê
7
8
6 5È
For CDN and Oceania
For Europe

–5 –
SPEC
CABLE ROUTING
ÈFasten the front brake switch lead with two plas-
tic bands.
ÉFasten the rear brake switch lead and handlebar
switch lead with two plastic bands.
ÊFasten the rear brake switch lead, handlebar
switch lead, and horn switch lead with two plas-
tic bands. (for Europe)
ËDo not pull the wire harness after fastening it.
ÌWhen installing the front fender, do not pinch the
coupler cover.
ÍPass the leads and wire harness through the
guides on the front fender as shown.
OFFRUN
ENG.STOP
LO
HI
0FF
LIGHTS
LIGHTS
0FF
HI
LO
ENG.STOP
OFF RUN
1 4
2 3
É
12
09
DC Ì
Ë
Í
A
B
Ê
7
8
6 5È
For CDN and Oceania
For Europe

–6 –
SPEC
CABLE ROUTING
1Front brake cable
2Throttle cable
3Rear brake cable
4Rear brake switch lead
5Handlebar switch lead
6Horn switch lead (for Europe)
7Wire harness
8Front brake switch lead
ÈPass the front brake cable and rear brake cable
through the cable guide. (for CDN and Oceania)
Pass the front brake cable, rear brake cable, and
horn switch lead through the cable guide. (for
Europe)
ÉRoute the rear brake cable to the inside of the
front fender bracket.
ÊPass the air duct inlet and outlet hoses between
the brake cables.
1 2 3
4
8
5
6
Î
È
É
Ê
Í
Ë
Ì
7

–7 –
SPEC
CABLE ROUTING
ËCross the front brake cables behind the steering
shaft. Route the right front brake cable in front of
the left front brake cable.
ÌPut the cover on the couplers, and then fasten a
plastic band around the middle of the cover.
ÍRoute the rear brake switch lead and the handle-
bar switch lead behind the throttle cable and the
rear brake cable.
ÎRoute the horn switch lead behind the coupler
cover, throttle cable, front brake cable, and rear
brake cable. (for Europe)
1 2 3
4
8
5
6
Î
È
É
Ê
Í
Ë
Ì
7

–8 –
SPEC
CABLE ROUTING
1Transmission case breather hose
2Throttle cable
3Front brake cable
4Main switch lead
5Wire harness
6Rectifier/regulator
7Horn lead (for Europe)
8Horn (for Europe)
9Starter motor lead
0A.C. magneto lead
AStarter motor
ÈFasten the wire harness, starter motor lead, and
transmission case breather hose to the frame
with a plastic band.
ÉRoute the wire harness, starter motor lead, and
the transmission case breather hose under the
frame cross member.
A B-B
7
7
Ô
1È2
3
4
Ë
5
6ÌÍ
Î
78
É
9
ÑÐ
0A
ÒÓÒ
Ê
B
A
B
Ï

–9 –
SPEC
CABLE ROUTING
ÊFasten the wire harness, starter motor lead, and
transmission case breather hose to the frame
with a plastic band. Be sure not to pinch the
transmission case breather hose. The end of the
plastic band should be toward the front of the
vehicle, facing inward.
ËPass the main switch lead and wire harness
through the hole in the front fender. Do not leave
any slack in the main switch lead and wire har-
ness under the front fender.
ÌFace the end of the transmission case breather
hose down.
ÍFasten the wire harness, starter motor lead, and
rectifier/regulator lead to the frame with a plastic
band. (for CDN and Oceania)
Fasten the wire harness, starter motor lead, rec-
tifier/regulator lead, and horn lead to the frame
with a plastic band. (for Europe)
ÎFasten the horn lead to the front fender bracket
with a plastic band just above the horn bracket.
(for Europe)
A B-B
7
7
Ô
1È2
3
4
Ë
5
6ÌÍ
Î
78
É
9
ÑÐ
0A
ÒÓÒ
Ê
B
A
B
Ï

–10 –
SPEC
CABLE ROUTING
Ï80 mm (3.15 in)
ÐFasten the starter motor lead and A.C. magneto
lead to the frame with a plastic band. The end of
the plastic band should be toward the rear of the
vehicle, facing inward.
ÑFasten the starter motor lead and A.C. magneto
lead with a plastic locking tie.
ÒFasten the A.C. magneto lead with the holders.
ÓRoute the A.C. magneto lead on top of the
crankcase.
ÔFace the end of the plastic band inward. (for
Europe)
A B-B
7
7
Ô
1È2
3
4
Ë
5
6ÌÍ
Î
78
É
9
ÑÐ
0A
ÒÓÒ
Ê
B
A
B
Ï

–11 –
SPEC
CABLE ROUTING
1Tail/brake light
2Tail/brake light lead
3Reverse relay
4Starting circuit cut-off relay
5Starter relay
6Positive battery lead
7Negative battery lead
8Transmission case breather hose
9Reverse switch
0Neutral switch lead
AReverse switch lead
BStarter motor lead
CBattery breather hose
DFuse holder
1
7
A 0
2È
Õ
3
D
C
B
Ó
Ñ
Ò
Ñ
4 5 É6ÊË7Ì8
A
A
Ô
Ï
Ð
ÎA09Í

–12 –
SPEC
CABLE ROUTING
ÈFasten the tail/brake light lead to the rear carrier
with a plastic band.
ÉPass the positive battery lead through the rear
hole in the rear fender.
ÊPass the negative battery leads through the front
hole in the rear fender.
ËFasten the wire harness with the holder.
ÌAlign the white tape of the wire harness with the
front end of the frame support as shown.
ÍRoute the fuel overflow hose in front of the trans-
mission case breather hose.
ÎInstall both the holder and the negative battery
lead terminal to the crankcase with the screw so
that the holder is in front of the terminal. Fasten
the neutral switch lead and reverse switch lead
with the holder.
ÏPass the fuel overflow hose between the swing-
arm and crankcase.
ÐThe end of battery breather hose should be
lower than the frame.
1
7
A 0
2È
Õ
3
D
C
B
Ó
Ñ
Ò
Ñ
4 5 É6ÊË7Ì8
A
A
Ô
Ï
Ð
ÎA09Í